The present invention relates generally to an intake manifold of an engine and, more particularly, it is concerned with a structure in which a multiple on-off valve mechanism having a plurality of on-off valves which are supported by a common shaft is incorporated in downstream end portions of individual intake passages which branch out from a joint portion.
Conventionally known arrangements include, for example, a structure disclosed in Japanese Unexamined Patent Publication No. 8-240123, in which on-off valves (flap valves) for regulating intake gas flow are provided in intake passages in an intake manifold that are connected to individual cylinders. In the structure of this Patent Publication, the individual on-off valves are mounted on a common shaft to form a multiple on-off valve mechanism and a driving device is connected to one end of the shaft at an outer side portion of the intake manifold, wherein the driving device rotates the shaft, causing the individual on-off valves to simultaneously open and close.
The structure of the Patent Publication is characterized in that the individual on-off valves joined to the shaft are accommodated in downstream end portions of the respective intake passages and supporting frames are fitted into the intake passages from their downstream end openings, the supporting frames serving to hold the shaft and secure it to the intake passages, so that the structure can be manufactured at low cost.
According to the structure described in the Patent Publication cited above, the multiple on-off valve mechanism is assembled into the intake manifold by first accommodating the individual on-off valves in specific parts of the downstream end portions of the respective intake passages and then fitting the aforementioned supporting frames in the intake passages in such a way that the on-off valves would not be displaced. As the supporting frames need to be formed such that they would accurately fit in the intake passages without any looseness, it is extremely difficult to fit the supporting frames after aligning them with the intake passages and on-off valves. Thus, there is room for improvement in assembling efficiency.
In addition, since the supporting frames hold and secure the shaft in the intake manifold when the supporting frames are fitted into the intake passages, there is a problem that resistance to rotation of the shaft tends to increase in the aforementioned structure.
In the light of the foregoing problems of the prior art, it is an object of the invention to provide an intake manifold of an engine that can improve the efficiency of assembling on-off valves into the manifold and reduce resistance to rotation of a shaft after assembly.
According to the invention, an intake manifold of an engine comprises a multiple on-off valve mechanism which is provided at downstream end portions of individual intake passages branching out from their joint portion, the multiple on-off valve mechanism having a plurality of on-off valves linked to a common shaft, wherein frame members formed separately from a manifold body are fitted in the downstream end portions of individual intake passage sections, the on-off valves are placed inside the individual frame members and the shaft is passed through the on-off valves in such a way that the frame members constitute parts of inside walls of the intake passages where the on-off valves are located, the frame members rotatably supporting the on-off valves and the shaft, and wherein a cutout is formed in a surrounding wall of each frame member, the cutout extending along the intake passage axis line all across the surrounding wall and thereby making each frame member expandable and compressible by elastic deformation.
In this construction, the on-off valves are assembled in the frame members, the frame members are fitted in the downstream end portions of the individual intake passage sections, and the shaft is assembled. This construction facilitates assembly of the intake manifold provided with the multiple on-off valve mechanism. Especially because the frame members are expandable and compressible by elastic deformation, the on-off valves can be easily fitted in the frame members and the frame members can be inserted into the downstream end portions of the intake passage sections with ease.
These and other objects, features and advantages of the present invention will become apparent upon reading of the following detailed description along with the accompanied drawings.